Researchers from the Netherlands asked 48 healthy older men to consume 20g of either whey, casein or casein hydrolysate to determine which had the greatest impact on building muscle (muscle protein synthesis). Leucine content was 2.5g in whey and 1.7g in both casein proteins.
For both casein groups, there was no difference in muscle protein synthesis response measured six hours after ingestion. However, the whey group increased muscle protein synthesis nearly two-fold more than the casein proteins.
Plasma leucine levels were highest after ingesting whey, intermediate after casein hydrolysate, and lowest after casein. There was a significant association between plasma leucine levels and muscle protein synthesis.
These findings provide evidence that the greater increase in muscle protein synthesis from whey protein is attributed to its rapid absorption and its higher leucine content.
In another study, researchers again compared whey and casein, but this time subjects ingested the protein after exercise.
Researchers wanted to determine which protein was best at promoting a better recovery response to resistance training.
Danish researchers had subjects perform a bout of resistance exercise, immediately after which they either consumed no food (control group), 20g of whey protein or 20g of casein.
Compared to the control group, both whey and casein groups increased muscle protein synthesis.
When examined over a six-hour post-exercise recovery period, both whey and casein groups showed similar increases.
However, during the first 30 minutes of the six-hour post recovery period, the muscle-building effect of whey was 25% higher than casein. But during the second half hour, casein was 32% higher than whey.
These findings suggest that whey promotes a rapid and large increase in muscle protein synthesis, but one that’s short-lived, compared to a more moderate and sustained effect of casein. Therefore, adding casein to a whey shake may keep you in a muscle-building state for a longer period of time than just taking whey alone.